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University of Minnesota
May 13, 2013
Sarah Hobbie is the University of MInnesota's newest member of the National Academy of Sciences.
Sarah Hobbie is elected to the National Academy of Sciences
It's easy to appreciate how green plants help keep the carbon cycle going. We can see them grow as they store carbon from carbon dioxide.
This puts a damper on the greenhouse effect, but it's only half the story, says Sarah Hobbie.
"I think it's easy to ignore or never learn about the other half of the carbon cycle, which is when carbon goes back to the atmosphere," explains Hobbie, a professor of ecology, evolution and behavior at the University of Minnesota. "But we don't see it because it is mostly done by microscopic fungi and bacteria."
Unlike them, however, Hobbie has not gone unnoticed. On April 30, 2013, her work on carbon cycling won her election to the National Academy of Sciences, an honor most American scientists rank second to the Nobel Prize.
"I'm pretty surprised. It wasn't anything I expected," she says. "I have many colleagues who are deserving."
Where all that litters is gold
A U faculty member since 1998, Hobbie has shone a light on the hidden world of grassland and forest soils and leaf litter, where microbes decompose organic matter. This releases CO2 and recycles carbon, nitrogen, phosphorus, and other nutrients. Without these microbes, we'd all be up to our ears in dead trees, if we didn't starve first.
Fossil fuel burning and other human actions alter the carbon cycle by releasing additional CO2, most of which is accumulating in the atmosphere. Any response by ecosystems that leads to changes in decomposition or plant growth rates can offset or augment the effects of fossil fuel use, Hobbie says.
"It's amazing teaching with Sarah because she combines top-notch science with incredible organization and care about the students."--Stephen Polasky, professor of applied economics and Academy member
"On land, about 60 billion metric tons of carbon are emitted every year from decomposition, compared to just nine billion or so from deforestation, cement production, and fossil fuel burning," she says. "So if we tweak it even a little, that could make a big difference."
A key question is whether airborne nitrogen--from fossil fuel combustion and fertilizers--nourishes the world's soil microbes and makes them produce CO2 faster. In experiments at the U's Cedar Creek Ecosystem Science Reserve, Hobbie found that higher nitrogen levels did indeed speed up the early stages of leaf litter decomposition. But in later stages, the litter decomposed 20 to 60 percent more slowly, depending on the form of nitrogen she added. She is now expanding the studies to grassland ecosystems worldwide to get a clearer picture.
"My work isn't geared to trying to slow down decomposition, but to trying to get all the pieces of the puzzle," Hobbie explains. "Part of what ecologists are trying to do is give society the best information so people can decide what to do about environmental problems."
Cleaner city water
Urban ecosystems also figure into Hobbie's work.
"Sarah has it all. She is a world-class researcher, a dedicated teacher and valued mentor for U of M biology students."--David Tilman, Regents Professor of ecology and Academy member
Along with colleagues, she surveyed 3,000 households in two Twin Cities metro-area counties to find the biggest sources of pollution from carbon, nitrogen, and phosphorus, with the goal of working with residents to reduce it. One striking result: About 20 percent of the households accounted for some 70 percent of the nitrogen fertilizer use, along with similarly disproportionate outputs of CO2 (from air travel) and phosphorus (from pet waste).
A very human reason for some households' high fertilizer use emerged.
"It's about green lawns," Hobbie says. "Keeping up appearances matters."
She also collaborates on efforts to improve urban water quality by other means, such as optimizing street sweeping schedules to cut the amounts of decaying leaves--and the nutrients they contain--that wash into streams.
"We're used to having good things happen, but not perfect things. And this is one of them. This is a perfect thing to happen."--Clarence Lehman, associate dean for research and graduate education, College of Biological Sciences
The next generation
"A lot of my undergraduate students won't go on to graduate school in ecology or biology, but they will be citizens of the world, says Hobbie. "I hope they can become better critical consumers of information. This is a hard time we live in, with all the unfiltered information out there."
She loves collaborating, in both research and teaching, and especially enjoys graduate students she considers smarter than herself "because that's how I learn."
With her election to the academy, Hobbie's influence can only grow.
When elected, "I realized this is a big responsibility, because suddenly, people who might not have listened to me before will do so now," she muses. "I'll have more of an opportunity to have an influence, and I hope to use that wisely."